Method and apparatus for reducing data collisions in a frequency hopping communication system

ABSTRACT

A method in a transmitter for data collision avoidance in an uncoordinated frequency hopping communication system is disclosed. The base station ( 104 ) first determines ( 304 ) that a first data set to be sent to a first device ( 105 ) and a second data set to be sent to a second device ( 107 ) are scheduled to be transmitted simultaneously on a first frequency of a frequency hop-set. The device then transmits ( 310 ) the first data set on the first frequency of the frequency hop-set. The base station delays ( 312 ) transmission of the second data set, and finally transmits ( 316 ) the second data set on a second frequency of a frequency hop-set.

FIELD OF THE INVENTION

The present invention relates generally to wireless communications, andmore particularly to eliminating data collisions in a frequency hoppingcommunication system.

BACKGROUND OF THE INVENTION

Wireless communication devices generally operate in either licensed RFbands or an unlicensed RF bands. Radiotelephone service providersgenerally acquire licenses to operate a wireless communication system inone or more of a plurality of licensed RF bands. These systems employmultiple methods to allow multiple access by multiple mobile stations ona common band of frequency channels. One such access technique,frequency division multiple access (FDMA), allows multiple access byassigning the mobile stations to different frequency channels within theRF band. Some of these systems employ frequency hopping, wherein data istransmitted to and from the intended mobile station while periodicallychanging the frequency channel. The periodic channel frequency hoppingoccurs on a regular time interval known as a frame. Coordinatedfrequency hopping systems use predetermined hopping patterns, orhop-sets, wherein the hop-sets are coordinated between all mobilestations to ensure that the signals to and from two or more mobilestations do not occur simultaneously on the same frequency channel.Uncoordinated frequency hopping does not coordinate the hop-set betweenmobile stations resulting in the periodic occurrence of simultaneoussignal transmission on the same frequency. Such simultaneoustransmissions are referred to as channel collisions. Data receptionerrors occurring during a channel collision are referred to as datacollisions. Uncoordinated frequency hopping within this type of systemis generally not used as the channel collisions and resultant datacollisions will occur. The FCC has prohibited coordinated frequencyhopping within the Industrial Scientific and Medical (ISM) bands inorder to avoid spectrum aggregation by a single type of service.

Systems such as Bluetooth and 802.11 wireless communication systems, forexample operate within the ISM bands. To avoid data collisions thesesystems may monitor the band and choose to operate only in unoccupiedsub-bands. These systems may also change sub-bands as the result of thedetection of interferer signal strength or the detection of signalingerrors indicative of a channel collision with another transmittingstation. However channel collisions still occur as devices must sensethe interference caused by a channel collision in order to change thefrequency sub-band.

Therefore, in order for a GSM system to be compliant with FCCregulations a change to the hopping channel assignment scheme is neededsuch that the hopping channel assignments are uncoordinated. Therefore,what is needed is a method for the elimination of data collision errorscaused by frequency hopping channel collisions in an uncoordinatedfrequency hopping system.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects, features and advantages of the present inventionwill become more fully apparent to those having ordinary skill in theart upon careful consideration of the following Detailed Description ofthe Drawings with the accompanying drawings described below.

FIG. 1 is an exemplary diagram of a communication system;

FIG. 2 is an exemplary block diagram of a wireless communication device;

FIG. 3 is an exemplary flow diagram of a data transmission method;

FIG. 4 is an exemplary flow diagram of a data reception method;

FIG. 5 is an exemplary flow diagram of a data reception method; and

FIG. 6 is an exemplary flow diagram of a data transmission method.

DETAILED DESCRIPTION OF THE DRAWINGS

A method for the elimination of data collision errors in anuncoordinated frequency hopping communication system is disclosed. Themethod comprises determining that a first data set, which is to be sentto a first device, and a second data set, which is to be sent to asecond device, is scheduled to be transmitted simultaneously on a firstfrequency, i.e. a channel collision. The data collision is avoidedbetween the two data sets, by transmitting the first data set on thefirst frequency hopping frequency, while the second data set is delayed,also known as muted. The first data set is thereby transmittedunambiguously and data collisions are avoided in the first device. Thefinal step is transmitting the second data set on a second frequencyhopping frequency, sequentially next in the frequency hop pattern at thenext frame. The second data set is thereby transmitted unambiguouslywith a delay of at least one frame. Thus the hopping channels areuncoordinated, since the original uncoordinated hopping sequences areunmodified except for the muting of the transmission to the seconddevice during the channel collision. Data collisions are avoided in thesecond device during the transmission of the first data set by adetermination that the second device is not the intended recipient, andsuspension of data reception until another frame.

Due to RF spectrum limitations, an increase in users and the cost of RFspectrum licenses, wireless telecommunications service providers canbenefit from using unlicensed RF spectrum to complement the licensedspectrum portion of their systems. Although the spectrum is unlicensed,use-requirements may still apply. One example is the use of unlicensedRF bands to augment GSM radiotelephone services. The GSM system can usecoordinated frequency hopping in which each mobile station in a celluses the same set of channel frequencies and hopping pattern, and aunique time offset of the hopping pattern determined by the mobileallocation index offset (MAIO). In this way the system can accommodateone communication signal for each hopping channel without the occurrenceof channel collisions within the same cell.

FIG. 1 is an exemplary diagram of a wireless communication system 100according to the present invention. The system 100 includes a basestation controller (BSC) 102, also known as a radio network controller(RNC) 102 in some systems, at least one base station 104, and a firstwireless device 105, also known as a mobile station (MS) 105, and asecond wireless device 107. The BSC 102 and the base stations 104 formthe radio access network (RAN) 106 portion of the system whichcommunicates with the wireless devices. A core network, which is coupledto the RAN, includes a mobile switching center (MSC) and may include aserving GPRS support node (SGSN). The core network (CN) 108 portion ofthe system, illustrated in FIG. 1, includes a first MSC 110 and a firstSGSN 112 for a first service provider. The system 100 may also include asecond MSC 114 and a second SGSN 116 for a second service provider. Inthe exemplary embodiment shown in FIG. 1, only two core networks areillustrated but it is understood by one skilled in the art that aplurality of core networks may be coupled to a RAN.

The base station 104 receives messages from the BSC 102 and transmitsthe messages to the intended wireless devices under an uncoordinatedfrequency hopping scheme. Communications between the base station 104and the first wireless device 105 share a first uncoordinated hop-setwhile the base station 104 and the second wireless device 107 share asecond uncoordinated hop-set. There is no coordination between the firstuncoordinated hop-set and the second uncoordinated hop-set, howeverthese hop-sets may comprise common frequency channels such thatfrequency channel collisions may occur. The wireless devices may bemobile stations or other user equipment that communicate with a servingnode, such as the exemplary base station 104 of the communication system100 in FIG.1. Each wireless device however is coordinated with the basestation 104 to necessarily form the communication link between the two.Information represented in the data sets which are to be transmitted tothe wireless devices either originate at the BSC 102, or are received atthe BSC 102 from the core network 108 to be relayed to the intendedwireless device. The information can be either packet-switched data orcircuit-switched data and the information may be voice information ordata information.

Turning to FIG. 2, a block diagram of a wireless communication device200 in accordance with one embodiment of the invention is shown. Thisembodiment can be a cellular radiotelephone incorporating the presentinvention. However, it is to be understood that the present invention isnot limited to this embodiment and may be utilized by other wirelesscommunication devices such as paging devices, personal digitalassistants, portable computing devices, and the like, having wirelesscommunication capabilities. In this embodiment a frame generator 202 anda microprocessor 204, combine to generate the necessary communicationprotocol for operating in a wireless communication system.Microprocessor 204 uses memory 206 comprising RAM 207, s EEPROM 208, andROM 209, which can be consolidated in one package 210, to execute thesteps necessary to generate the protocol and to perform other functionsfor the wireless communication device, such as writing to a display 212,accepting information from a keypad 214, or controlling a frequencysynthesizer 226 to attune the device to the appropriate frequency in afrequency hopping pattern. The memory may also include a SIM card 232.In situations where the wireless device is used for voice transmissions,the frame generator 202 processes audio transformed by audio circuitry218 from a microphone 220 and to a speaker 222.

FIG. 2 also shows at least one transceiver 227 comprising receivercircuitry 228, that is capable of receiving RF signals from at least onebandwidth and optionally more bandwidths. The receiver 228 mayoptionally comprise a first receiver and a second receiver, or onereceiver capable of receiving in two or more bandwidths. The receiver228, depending on the mode of operation, may be tuned to receive PLMRS,AMPS, GSM, EGPRS, CDMA, UMTS, WCDMA, Bluetooth, or WLAN, such as 802.11communication signals for example. The transceiver 227 includes at leastone transmitter 234. The at least one transmitter 234 may be capable oftransmitting to one device or base station in one frequency band andpotentially on multiple frequency bands. As with the receiver 228, dualtransmitters 234 may optionally be employed where one transmitter is forthe transmission to a proximate device or direct link establishment toWLAN's and the other transmitter is for transmission to the base station108.

The wireless communication device 200, which can be adapted tocommunicate in a frequency hopping wireless communication, may alsocomprise a channel collision detection module 224 that detects whenreceived messages are not intended to be received by the mobile station200 and a transmission scheduling module 225 both coupled to themicroprocessor 204.

A base station 104 of the wireless communication system can include atransmitter 120 and a receiver 122 for communicating with a plurality ofwireless communication devices. The base station 104 can also include amessage reception module 124, that receives messages from the corenetwork which are to be transmitted to one of a plurality of wirelesscommunication devices. The base station may also include a frequency hoppattern generation module 126. The frequency hop pattern generationmodule 126 determines the frequency hop-set pattern for each device ofthe plurality of devices. The frequency hop-set patterns areuncoordinated from device to device. The base station 104 can alsoinclude a channel collision detection module 128 that detects whenreceived messages are scheduled to be transmitted on the same frequencyat the same time and a message scheduling module that reschedules ordelays transmission of a data set that was determined to collide withanother data set.

FIG. 3 shows an exemplary flow diagram 300 illustrating how a first dataset is received 302 at the base station 104 for transmission to theintended mobile station. The intended mobile station can be the firstwireless device 105 in this exemplary embodiment. In step 302, the firstdata set is received at a first time on a first frequency of a firstuncoordinated frequency hop-set. Similarly, a second data set is alsoreceived at the base station 104 for transmission to the intended mobilestation, the second mobile station 107 in this exemplary embodiment. Thefirst data set and the second data set do not necessarily arrive at thebase station 104 at the same time. It is envisioned that they can infact be received independently. The second data set can be alsoscheduled to be sent at the first time on the first frequency of asecond uncoordinated frequency hop-set. The base station 104 candetermine in step 304 that a data collision will occur as both the firstand the second data set are scheduled to be transmitted on the samefrequency at the same time. In step 308, the base station 104 candetermine which data set to send first or at all. In step 310, the firstdata set is then transmitted to the first wireless device 105 in thisexemplary embodiment. This provides for an unambiguous transmission tothe first wireless device 105. In step 312, the second data set isdelayed, or muted and not transmitted at the scheduled time or on thescheduled frequency. If the second data set is to be delayed, in step314, the second data set may be delayed one cycle in the frequencyhop-set. In step 316, the second data set can then be sent to the seconddevice at the delayed time on the next frequency. If in step 304 thebase station 104 determines that a collision will not occur, the basestation 104 transmits, in step 306, both data sets as scheduled inaccordance with each respective hop-set. The second data set may also bediscarded instead of transmitted.

Although two data sets are used for exemplary purposes throughout thisdisclosure, it is envisioned that a plurality of data sets may bescheduled to be transmitted simultaneously and on the same frequency asthe individual frequency hop-sets associated with each device areuncoordinated between the devices. As the number of wireless devicescommunicating in the communication system increases, the potential fordata collisions also increases. Therefore the base station 104 mustcheck the scheduling of all messages to be transmitted, in accordancewith the above method, to avoid collisions.

FIG. 4 is an exemplary flowchart 400 outlining the operation of awireless device according to an exemplary embodiment. For example, thesecond wireless device 107 can be the intended recipient of the seconddata set from the base station 104. As the base station 104 has delayed312 the transmission of the second data set, the second device 107 canreceive 402 the first data set during the scheduled time the seconddevice 107 is supposed to receive the second data set. If, step 404, thesecond wireless device 107 determines the first data set is actuallyintended for the second wireless device 107, in step 406, the secondwireless device 107 processes the data. If in step 404, the secondwireless device 107 determines that it is not the intended recipient forthe data transmitted by the base station, i.e. the first data set, thefirst data set is discarded 408 or reception is suspended.

Continuing with reference to FIG. 4, the second device 107 can then tune410 to the next scheduled frequency in the hop pattern allowing thatdevice to receive 412 the second data set at the next frequency, at thenext scheduled frame. The next frequency in the hopping pattern is thenext scheduled frequency in the hop-set, such that the hopping patternresumes at the next scheduled frame. In this way the two hoppingpatterns, a first hopping pattern for the first device 105 and a secondhopping pattern for the second device 107, are uncoordinated hoppingpatterns since the hopping patterns are unaltered after the occurrenceof a channel collision.

The base station 104 should determine which data set should betransmitted after determining 304 that a channel collision will occur.In one exemplary embodiment, the base station 104 or the base stationcontroller 102 can send the data set received first in time at the basestation 104 or the base station controller 102. In this exemplaryembodiment, the data sets are processed on a first in first out (FIFO)basis. In another exemplary embodiment, the data set to be sent first israndomly selected. If multiple data sets are scheduled to collide, allexcept one data set would have to be rescheduled. It should be notedthat multiple transmissions can occur at the same time. However,multiple transmissions can not occur at the same time on the samefrequency without causing data collisions and resultant data errors inthe wireless device receivers. In another embodiment, priority is givenaccording to the radiated power at the base station 104. A higherpriority is assigned for example to a device that requires higherradiated power at the base station 104. It may also be the case that thehigher priority is assigned to a device that requires lower radiatedpower at the base station 104. In yet another embodiment, priority isgiven according to the needs of the wireless device, whereby voice datamay be given higher priority than other types of data, for example. Itis understood by one skilled in the art that there are a plurality ofmethods for determining which data set to send and in what order, andthe disclosure is not limited to those exemplary embodiments listedherein.

FIG. 5 is an exemplary flowchart outlining a method 500 for determiningthat the data is not intended to be received by either of the exemplaryfirst wireless device 105 or the second wireless device 107. Forexample, this process may be used in step 404 of the flowchart 400. Inthis embodiment, a unique sub-channel code can be assigned 502 to eachwireless device using the hop-set. The unique sub-channel code can beinserted 504 into each transmission. In this exemplary embodiment, theunique sub-channel code can be included in a control field in thereceived data set. The unique sub-channel code allows each device todetermine which data set, the first data set or the second data set inthe exemplary embodiment, is intended to be received by the respectivedevice. The wireless device 105, 107 can then decode 506 the controlfield upon reception of the data set and determine 508 if the uniquesub-channel code in the received data set matches the unique sub-channelcode assigned to the wireless device by the base station 104. If theunique sub-channel code matches 510, then device processes 512 the data.If the unique sub-channel code does not match 514, the data set isdiscarded 516.

For example, in an exemplary GSM system, a GSM traffic channel (TCH)might be modified to include a temporary mobile station identity code(TMSIC), which is the unique sub-channel code having a unique value forevery wireless device receiving a data set, i.e. data transmissions,from the base station on a particular hop-set of hopping frequencieschannels. Upon decoding the TMSIC the second mobile station willdetermine that the received TMSIC is different that its TMSIC assignmentand discard the received data or suspend reception.

Referring to FIG. 6, in another exemplary embodiment flowchart 600, thewireless devices, such as the first and second wireless device 105, 107,receive 602, from the base station 104, a unique priority code which isassigned to each wireless device using the hop-set of frequency hoppingchannels. The wireless device, 105, 107 then receive 604 from the basestation 104 the channel frequencies and hopping patterns of all wirelessdevices using a hop-set. The received frequencies and hopping patternsare used by the wireless devices 105, 107 to predict or determine whenchannel collisions will occur. For example when the first wirelessdevice 105 detects 606 a channel collision, the first device 105 can usea predetermined rule set to determine 608 the intended recipient of theinformation transmitted by the base station 104. The predetermined ruleset assures that only one recipient is assigned during a channelcollision.

In one exemplary embodiment of this approach, the first wireless device105 is assigned a device priority of “1”, and a device priority of “0”is assigned to all other wireless devices using the hop-set. The firstdevice 105 will receive 610 the first message which has the higherpriority code. The first device 105 will discard 612 any message with a“0” priority. If there will not be a channel collision, the message isreceived and processed 614. In this embodiment, multiple devices can begiven the priority of “1” and when a channel collision is detected, therule set determines which device with the “1” priority to receive thedata set, with all other data set transmissions being delayed until thenext scheduled frame. In another exemplary embodiment the devicepriority might automatically change according to predetermined rulesafter each channel collision, such that the mobile stations alternateusing the channel during channel collisions. Upon determining that achannel collision will occur and that the transmitted data set isintended for a different wireless device, the second device suspendsreception. The priority of “1” and “0” are exemplary values and thevalues may be integrated over a range of values for example.

Complimentary to the mobile station operation, after the base stationdetects that the channel collision will occur; the base station mustdetermine if the channel collision involves data being sent to at leastone device with a higher priority code. The base station will determineif a first message has a priority code higher than a second message. Inthis exemplary embodiment, only the first wireless device with thepriority of “1” will receive the transmission of the first message whena channel collision occurs. The base station will send the first messagewhich has the higher priority code and delay the message or messageswith the lower priority code.

In the above exemplary embodiments, the methods allow for the avoidanceof data collisions in the downlink transmissions from base station tomobile station, i.e. wireless device. Analogous techniques may beapplied for avoiding data collisions on the uplink transmissions, i.e.transmissions between mobile stations and the base station. This appliesto the situation in which the uplink and down-link hop sets areuncoordinated. However it is anticipated that coordination of up-linkand down-link hop-sets will be allowed. In the cases such where thedownlink and uplink channels are assigned in pairs, one exemplaryembodiment provides a method where the uplink channel assignment followsthe downlink assignment on the same frequency channels. In anotherexemplary embodiment, such as in the GSM case, the uplink channelfollows the downlink channel with a fixed frequency offset. According tothis approach, whenever a downlink channel collision occurs there willnecessarily be a corresponding uplink collision. Thus, in this exemplaryembodiment, when a wireless device receives a downlink data set during achannel collision as in accordance with one of the approaches describedabove, it will then transmit its uplink data set on the scheduled uplinktransmission period, whereas if a wireless device does not receive adata set during a channel collision it will refrain from transmittingits data set on the scheduled uplink period, and wait until the nextscheduled uplink period to transmit the data set on the next channelfrequency in the hop-set, thereby avoiding an uplink data collision.

While the present inventions and what is considered presently to be thebest modes thereof have been described in a manner that establishespossession thereof by the inventors and that enables those of ordinaryskill in the art to make and use the inventions, it will be understoodand appreciated that there are many equivalents to the exemplaryembodiments disclosed herein and that myriad modifications andvariations may be made thereto without departing from the scope andspirit of the inventions, which are to be limited not by the exemplaryembodiments but by the appended claims.

1. A method in a transmitter for data collision avoidance in anuncoordinated frequency hopping communication system comprising:determining that a first data set to be sent to a first device and asecond data set to be sent to a second device are scheduled to betransmitted simultaneously on a first frequency; transmitting one of thefirst data set and the second data set on the first frequency; delayingtransmission of an other of the first data set and the second data set;and transmitting the other of the first data set and the second data seton a second frequency.
 2. The method according to claim 1, delayingtransmission of the second data set temporally to the next scheduledtransmission time.
 3. The method according to claim 2, wherein the firstfrequency is one of a plurality of frequencies of a first frequencyhopping pattern.
 4. The method according to claim 2, wherein the secondfrequency is one of a plurality of frequencies of a second frequencyhopping pattern.
 5. The method according to claim 3, wherein the secondfrequency is one of a plurality of frequencies of a second frequencyhopping pattern.
 6. The method according to claim 5, further comprisingtransmitting the second data set on a frequency which is sequentiallynext in a frequency hop-set.
 7. The method according to claim 3, furthercomprising, prior to, transmitting one of the first data set and thesecond data set, randomly selecting either the first data set or thesecond data set to be transmitted first.
 8. The method according toclaim 7, wherein transmitting one of the first data set and the seconddata set further comprises transmitting the randomly selected data setof the first or second data set during a scheduled transmission frameand on a scheduled transmission frequency, and wherein delaying furthercomprises delaying the data set of the first or second data set notrandomly selected to the next scheduled transmission frame.
 9. Themethod according to claim 8, wherein transmitting the other of the firstdata set and the second data set further comprises transmitting the dataset not randomly selected at the next scheduled frame and on the nextscheduled transmission frequency.
 10. The method according to claim 9,further comprising assigning a first sub-channel code to the firstdevice.
 11. The method according to claim 10, further comprisinginserting the sub-channel code, that correlates to the first sub-channelcode assigned to the first device, into the first data set to betransmitted.
 12. The method according to claim 11, further comprisingassigning a second sub-channel code to the second device.
 13. The methodaccording to claim 12, further comprising inserting the secondsub-channel code, that correlates to the second sub-channel codeassigned to the second device into the second data set to be transmittedto the second device.
 14. A method in a transmitter for data collisionavoidance in an uncoordinated frequency hopping communication systemcomprising: determining that a first data set to be sent to a firstdevice and a second data set to be sent to a second device are scheduledto be transmitted simultaneously on a first frequency; transmitting thefirst data set on the first frequency; and discarding the second dataset.
 15. A method in a transmitter for data collision avoidance in anuncoordinated frequency hopping communication system comprising:receiving, from a base station, a channel frequency set and hoppingpatterns of all wireless devices in the frequency hopping communicationsystem using a hop-set; determining when a channel collision will occurusing the received channel frequency set and the hopping patterns;transmitting a first data set on the first frequency; and delayingtransmission of a second data set.
 16. A method in a wirelesscommunication device to eliminate data collisions in an uncoordinatedfrequency hopping communication system comprising: receiving a firstdata set on the first frequency hopping frequency; determining that thefirst data set was not intended to be received by the device; delayingtransmission of a second data set; and transmitting the second data seton a second frequency of a frequency hopping pattern.
 17. The methodaccording to claim 16, wherein the step of determining that the firstdata set was not intended to be received by the device comprises:comparing a first sub-channel code in said first data set to asub-channel code assigned to the wireless communication device.determining that the first sub-channel code in said first data set doesnot match the sub-channel code assigned to the wireless communicationdevice.
 18. The method according to claim 17, wherein the second dataset is transmitted on a second frequency which is sequentially next in afrequency hopping pattern.
 19. A method in a wireless communicationdevice to eliminate data collisions wherein transmissions are made in anuncoordinated frequency hopping scheme such that the downlink channelsand uplink channels are assigned in pairs, and wherein the uplinkchannel assignment follows the downlink assignment and uplink channelcollisions occur following downlink channel collisions, said methodcomprising: determining that a downlink channel collision has occurred;refraining from transmitting an uplink data set during the scheduleduplink period; and transmitting the uplink data set on the nextscheduled uplink period thereby avoiding an uplink channel collision.20. The method according to claim 19, wherein determining that adownlink channel collision has occurred further comprises determiningthat a downlink data set received by the device was not intended to bereceived by the device.
 21. The method according to claim 20, whereindetermining that a downlink channel collision has occurred furthercomprises determining that a sub-channel code included in the downlinkdata set received by the device does not match an assigned sub-channelcode.
 22. The method according to claim 21, wherein determining that adownlink channel collision has occurred further comprises determiningthat a priority code does not match an assigned priority code.
 23. Amethod in a transmitter for data collision avoidance in a frequencyhopping communication system comprising: determining that a first dataset to be sent to a first device and a second data set to be sent to asecond device are scheduled to be transmitted simultaneously on a firstuncoordinated frequency hopping frequency; transmitting the first dataset on the first frequency hopping frequency; delaying transmission ofthe second data set; transmitting the second data set on a secondfrequency hopping frequency; transmitting a third data set to a thirddevice on a first coordinated frequency hopping frequency.
 24. A basestation in a wireless communication system comprising: a messagereception module, wherein messages received by the message receptionmodule are to be transmitted to one of a plurality of communicationdevices; a frequency hop pattern generation module; a channel collisiondetection module that detects when received messages are scheduled to betransmitted on the same frequency at the same time; a message schedulingmodule; and a message transmitter.
 25. A mobile station adapted tocommunicate in a frequency hopping wireless communication systemcomprising: a receiver module, wherein messages are received on afrequency of an uncoordinated frequency hopping hop-set; a channelcollision detection module that detects when received messages are notintended to be received by the mobile station; a transmission schedulingmodule; and a transmitter.